This may be considered as the breakthrough for many of current ideas, algorithms and Internet technologies. It started Paul Baran in 1960s funded by Advanced Research Projects Agency (ARPA), an organization of the united States Defense Department and, therefore, named as Advanced Research Projects Agency Network (ARPANET) predecessor of the modern Internet. It was world's first fully operational packet switching computer network and the world's first successful computer network to implement the TCP/IP reference model that was used earlier by ARPANET, before being used in the Internet. The ARPANET is the first network that planed the seed of interent.

ARPANET was built to accommodate research equipment on packet switching technology and to allow resource sharing for the Department of Defense's contractors. The network interconnected research centers, some military bases and government locations. It soon became popular with researchers for collaboration through electronic mail and other services.

• It is basically a WAN. It was developed by the ARPA (Advanced Research Project Agency) in 1968 which is the research arm of 000.• ARPANET was designed to service even a nuclear attack.• Before ARPANET, the networks were basically the telephone networks which operated on the circuit switching principle.• But this network was too vulnerable, because the loss of even one line or switch would terminate all the conversations.• ARPANET used the concept of packet switching network consisting of subnet and host computers.• The subnet was a datagram subnet and each subnet consists of minicomputers called IMPs (Interface Message Processors).• Each node of the network used to have an IMP and a host connected by a short wire.• The host could send messages of upto 8063 bits to its IMP which would break them into packets and forward them independently toward the destination.• The subnet was the first electronic store-and-forward type packet switched network. So each packet was stored before it was forwarded.

• The software for ARPANET was split into two parts namely subnet and host.

• In 1974 the TCP/IP model and protocol were invented specifically to handle communication over internetwork because more and more networks were getting connected to ARPANET.

• The TCP/IP made the connection of LANs to ARPANET easy.

• During 1980s so many LANs were connected to ARPANET that finding hosts became increasingly difficult and expensive.

• So DNS (Domain Naming System) was created for organizing machines into domains and map host names onto IP address.

• .In 1983 the management of ARPANET was handed over to the Defense Communications Agency (DCA) which separated the military portion into a separate MILNET.

• By 1990 the ARPANET was shut down and dismantled, however MILNET continues to operate.